Well, "Obsession" got it enormously wrong. The specified amount of antimatter was an ounce, which would react with matter with a maximum of 1.22 megatons of energy (according to this calculator
). That's about equal to the maximum yield of the most powerful bomb
currently in active service in the US arsenal. But it's an eighth the size of the Tunguska event, and a fortieth the size of the largest nuclear bomb ever detonated on Earth -- neither of which ripped away any significant amount of our planet's atmosphere.
Basically Star Trek
has a very bad track record when it comes to antimatter yields. Sometimes it says a tiny amount would destroy a planet or a star system -- but then it gives us something like the climax of ST V where an antimatter-warhead photon torpedo is detonated less than 30 meters behind Kirk, Spock, and McCoy and it does nothing but knock them over.